With respect to a catalyst which is used when isobutylene and/or tertiary butanol are subjected to a vapor-phase catalytic oxidation so as to produce methacrolein and/or methacrylic acid, and a catalyst which is used when propylene is subjected to a vapor-phase catalytic oxidation so as to produce acrolein and/or acrylic acid, a number of proposals have been made. These proposals relate primarily to elements constituting the catalyst and to the ratios thereof.
The above vapor-phase catalytic oxidation is an exothermic reaction, which causes thermal storage in a catalyst layer. A high temperature local zone which results from the thermal storage is referred to as a “hot-spot”. An excessive high temperature of this zone causes excessive oxidation, whereby the yield of an object product is decreased. Therefore, in the industrial operation of the above oxidation, the inhibition of the temperature of a hot-spot is a serious problem. In particular, when concentrations of isobutylene and/or tertiary butanol (which may be referred to as “isobutylene and the like”) or propylene in a raw material gas are increased so as to increase the productivity, the temperature of a hot-spot tends to be elevated, and therefore, reaction conditions therefor are actually subjected to large constraints.
Therefore, in order to industrially produce (meth)acrolein and/or (meth)acrylic acid with a high yield, it is very important to control the temperature of a hot-spot zone. Furthermore, in particular, when a solid oxidation catalyst including molybdenum is used, it is important to prevent a generation of the hot-spot because the molybdenum component is apt to easily sublimate.
Additionally, the term “(meth)acrolein” means “methacrolein and/or acrolein”, and the term “(meth)acrylic acid” means “methacrylic acid and/or acrylic acid”.
Heretofore, several methods of controlling the temperature of a hot-spot zone have been proposed. For example, JP-A-3-176440 discloses a method which comprises filling a reactor with a plural kinds of catalysts, which are different from each other on activities and have been prepared by varying their compositions, so that the activities are increasingly enhanced from the inlet side of a raw material gas toward the outlet side thereof, and passing a raw material gas including oxygen, isobutylene and the like through the catalysts layer. JP-A-55-113730 discloses a method which comprises filling a reactor with a plural kinds of catalysts, which are different from each other on activities and have been prepared by varying their compositions, so that the activities are increasingly enhanced from the inlet side of a raw material gas toward the outlet side thereof, and passing a raw material gas including oxygen and propylene through the catalysts layer. JP-A-8-92147 discloses a method which comprises controlling a flow of a heating medium so that a temperature of a heating medium bath be elevated by 2° C. to 10° C. between the inlet port of a multi-tubular type of fixed bed reactor having the heating medium bath and the outlet port thereof, when propylene is subjected to a vapor-phase oxidation into acrolein by using the reactor.
Each of these methods is the one in which the rate of reaction per unit volume at an inlet side for a raw material gas in a catalyst layer within a reactor is lowered so as to control a calorific value of reaction per unit volume, so that the temperature of a hot-spot zone can be lowered.
Furthermore, JP-A-2001-55355 discloses a method of producing an unsaturated nitrile and/or an unsaturated carboxylic acid, which comprises subjecting a hydrocarbon to a-vapor-phase catalytic oxidation in the presence of a compound metal-oxide catalyst including, as an essential ingredient(s), molybdenum, vanadium, and at least one element selected from the group consisting of tellurium and antimony, wherein the temperature is elevated in an atmosphere in which oxygen and/or a combustible gas are substantially included, until the temperature of the catalyst layer reaches a temperature at which a reaction can be initiated. Besides, in comparative example of the specification thereof, a method of elevating the temperature in an atmosphere of air is also disclosed.